Under current art, a device is able to connect to a docking station that may have multiple peripherals attached to it, such as a keyboard, mouse, display, etc. While docked, the device is able to charge any battery it may have, assuming that the dock is powered in some way, and also use the peripherals for input and output. Such a device that controls the peripherals is known as the host device.
Some devices, such as most currently available laptops automatically act as host devices as soon as they are connected to a docking station. This is due to the hardware, such as the connection ports available, or due to the software installed in the laptop. For example, most current laptops only have Type-A USB connection ports. According to current USB technology, the Type-A end of a USB cable must be connected to the host device and cannot be functionally connected to a peripheral. Similarly, some devices, such as external hard drives, are only able to act as peripherals. Again, this limitation may be imposed by hardware, such as the provision of a Type-B socket for a USB cable, or by software.
There are also devices that are able to act both as hosts and peripherals, following the USB OTG protocol. For example, many smartphones can act either as host devices in their own right or as external storage when connected to a host device such as a laptop. Their mode of operation is dictated by the state of the ID pin which only exists on the micro connectors, but not the standard connectors and so doesn't have a corresponding wire in a normal USB cable. If the connector leaves this pin floating, then the OTG device remains in peripheral mode, but if the pin is pulled to ground then the OTG device is connected to the connector in host mode.
A new Type-C USB connector functions such that either end can be connected to either one of a host or a peripheral. There may still be limitations on a device's behaviour based on its own capabilities, or it may switch its role for itself. In the USB Type-C case, the host and peripheral are identified by the voltage on a CC connection while the connection between the devices is being detected. This voltage difference is created by the use of pull-up resistors, which raise the voltage, and pull-down resistors, which lower it. If one device (“Device 1”) detects a low voltage on the CC connection with the other device (“Device 2”), Device 1 knows that Device 2 is to connect as a peripheral device. Likewise, if Device 2 detects a high voltage on the CC connection with Device 1, it knows that Device 1 is to act as host device. A dual-mode device automatically switches between its pull-up and pull-down resistors during connection until it finds a mode that is compatible with the device to which it is connected.
Presently known USB docking stations have a single upstream USB Type-B port into which a Type-B plug can be inserted with a Type-A plug on the other end of the USB cable being plugged into a USB Type-A port on the device, such as a laptop. Docking stations are also commonly used to charge mobile phones from their downstream USB ports. However with the increase in computational power in mobile phones, and utilising the OTG protocol, mobile phones can become hosts in themselves, that is, a mobile phone could be plugged into the upstream USB Type-B port of the docking station and control the workstation peripherals instead, whilst also charging at the same time.
However, if a user has a phone plugged into the USB Type-B port of the docking station, and then wants to utilise the increased capabilities of a laptop device, the phone will have to be unplugged from the USB Type-B port so that the laptop can be plugged into it, and if it is to continue charging, the mobile phone will then have to be plugged into a downstream USB Type-A port in the docking station. This is not convenient for the user.